The present invention relates to a method of manufacturing a poly-V pulley, used for a V-belt for transmitting rotary power.
A poly-V pulley which is formed into the shape of a two-part arrangement of poly-V grooves, i.e., a small-diameter poly-V groove and a large diameter poly-V groove is known. Generally, such a poly-V pulley is made of cast iron. However, the poly-V pulley made of cast iron is heavy. Moreover, the poly-V groove is formed by a cutting operation, thereby scattering cut powder in the workshop, and worsening the working environment. Furthermore, cutting operations require more time, thereby decreasing efficiency of the work.
An object of the present invention is to provide a method of manufacturing a poly-V pulley made of metal sheet, which has two poly-V grooves having different diameters, i.e., a small-diameter and a large diameter, and which can be produced from a thick flat-plate material Subsequently, the poly-V pulley is more durable, more lightweight and cheaper than the poly-V made of cast iron. Moreover, it can be easily and efficiently produced.
A method of manufacturing a poly-V pulley including a small-diameter cylindrical portion, a supporting base portion, and a large-diameter cylindrical portion, the small-diameter cylindrical portion having a small-diameter poly-V groove on an outer surface thereof, the supporting base portion having a shaft insertion hole at the center thereof, and the large-diameter cylindrical portion having a large-diameter poly-V groove on the outer surface thereof, which is disposed consecutively and concentrically with the small-diameter cylindrical portion via a stepped portion on the other end in the axial direction of the small-diameter cylindrical portion, comprises the steps of:
bending a circular flat-plate material provided with the shaft insertion hole at the center thereof, thereby forming a first forming body whose section is dish-shaped, including the supporting base portion and a conical peripheral wall consecutively disposed in a widening state from an outer end of the supporting base portion to the outside,
extending the conical peripheral wall in the widening end direction, and decreasing the thickness thereof, thereby forming a second forming body whose section is deep dish-shaped,
drawing the conical peripheral wall of the second forming body, whose thickness is decreased, thereby forming the small-diameter cylindrical portion and the large-diameter cylindrical portion, and
rolling-shaping respectively the small-diameter poly-V groove on the outer periphery of the supporting base portion and the outer surface of the small-diameter cylindrical portion, and the large-diameter poly-V groove on the outer surface of the large-diameter cylindrical portion by means of rolling.
In the method of manufacturing a poly-V pulley according to the present invention, in extending step, only the thickness of the conical peripheral wall is decreased, whereby the supporting base portion is extended so as to keep the great thickness of the flat-plate material intact, thereby producing the supporting base portion having necessary and enough strength so as to engage the crankshaft or the like therein. Moreover, the conical peripheral wall is previously extended, thereby decreasing the thickness thereof so as to draw the small-diameter cylindrical portion and the large-diameter cylindrical portion. Therefore, the drawing process is easily performed. Moreover, the conical peripheral wall is previously bent, whereby it is formed in an inclined and widening state. As a result, the present invention facilitates drawing process in comparison with the case of forming the small-diameter cylindrical portion and the large-diameter cylindrical portion from the flat-plate by direct drawing process.
Such a poly-V pulley made of the metal sheet can be economically, simply and efficiently produced, which is more durable and lightweight than the poly-V pulley made of cast iron.
Moreover, the method of manufacturing a poly-V pulley includes the steps of:
preparing a rotary upper die whose lower end surface is processed as a supporting base portion holding surface, a rotary lower die which is processed so as to have a conical shape with a top surface, namely, which includes a flat supporting base portion receiving surface and a conical slope-like peripheral wall receiving surface, and a side roller, in said extending step,
holding the supporting base portion of the first forming body between the supporting base portion holding surface and the supporting base portion receiving surface,
mounting the conical peripheral wall of the first forming body on the receiving surface of the peripheral wall,
rotating the first forming body together with the upper and lower rotary dies around the axis of the upper and lower rotary dies, while firmly pressing the outer periphery of the side roller against the outer periphery of the conical peripheral wall in the radial direction,
rotating the side roller around the axis thereof while moving it to the lower direction of a slope of the peripheral wall receiving surface, and
easily extending only the conical peripheral wall in the direction of the widening end in a decreased thickness state.
The poly-V grooves are shaped respectively on the outer peripheral surface of the small-diameter cylindrical portion and that of the large-diameter cylindrical portion by means of rolling through separate steps, thereby shaping the respective poly-V grooves accurately.
Moreover, the employed flat-plate material is provided boss portion disposed at the center thereof, which is protrusively integrated with the flat-plate material. Therefore, the boss portion has the same thickness as that of the flat-plate material in the same way the supporting base portion does, thereby ensuring a sufficient joining strength for joining it with the shaft.